One-dimensional wavefront sensor development for tomographic flow measurements

Optical diagnostics are extremely useful in fluid mechanics because they generally have high inherent bandwidth, and are nonintrusive. However, since optical probe measurements inherently integrate all information along the optical path, it is often difficult to isolate out-of-plane components in 3D flow events. It is also hard to make independent measurements of internal flow structure. Using an arrangement of 1D wavefront sensor, we have developed a system that uses tomographic reconstruction to make 2D measurements in arbitrary flow. These measurements provide complete information in a plane normal to the flow. We have applied this system to the subsonic free jet because of the wide range of flow scales available. These measurements rely on the development of a series of 1D wavefront sensors that are used to measure line-integral density variations in the flow of interest. These sensors have been constructed using linear CCD cameras and binary optics lenslet arrays. In designing these arrays, we have considered the coherent coupling between adjacent lenses and have made comparisons between theory and experimental noise measurements. This paper will present examples of the wavefront sensor development, line-integral measurements as a function of various experimental parameters, and sample tomographic reconstructions.